This invention relates generally to control of turbocharged diesel engines that propel motor vehicles, and in particular to control of a variable nozzle turbocharger of such an engine.
A turbocharger is one type of device that is used to supercharge an internal combustion engine. A diesel engine that is supercharged by a turbocharger is sometimes referred to as a turbocharged diesel. A turbocharger comprises a turbine that is powered by engine exhaust gas and coupled by a shaft to operate a compressor that boosts pressure in the engine air intake system downstream of the compressor. One way to control boost pressure is to control turbine operation.
There are several different forms of turbine control. One form of control involves the construction of the turbocharger itself. A turbocharger that has a variable geometry, or variable nozzle, is capable of changing the manner in which exhaust gas that flows through the turbocharger interacts with the turbine, and hence controlling the pressure, i.e. boost, that the compressor creates in the engine intake manifold. One type of variable geometry, or variable nozzle, turbocharger comprises movable vanes whose positions are selectively controlled to in turn selectively control the nature of exhaust gas interaction with the turbine, and hence the boost pressure developed by the turbocharger. The turbocharger includes a device for interfacing an electric control with the movable vanes. That device comprises an electromechanical actuator having a solenoid for setting vane position according to the extent to which the solenoid is electrically energized. With the solenoid placed under the control of the engine electronic control system, the extent to which the solenoid is energized, and hence vane position, are determined by the degree of modulation of a pulse width modulated (PWM) signal created by the electronic control system. The device may utilize a medium like fluid power, hydraulics for example, that is controlled by the solenoid actuator to impart movement to the vanes.
U.S. Pat. Nos. 4,428,199; 4,660,382; 4,671,068; 4,685,302; 4,691,521; 4,702,080; 4,732,003; 4,756,161; 4,763,476; 4,765,141; 4,779,423; 5,123,246; 5,867,986; 6,000,221; and International Application WO 99/23377 relate to control of turbocharged internal combustion engines. Certain of those documents relate to control of variable geometry turbochargers. Both documents WO 99/23377 and 6,000,221 disclose systems for control of the variable geometry of a turbocharger utilizing a signal from a turbocharger vane position sensor as feedback in closed-loop control of the vanes.
The present invention is distinguished by a closed-loop control system for controlling boost without a vane position sensor by utilizing certain data already available in an engine control system.
Certain of the documents disclose systems that employ PID functions for control purposes.
The present invention is distinguished from those systems by a P-LI-D function in which the integration function is selectively, or conditionally, employed depending on prevailing conditions.
One aspect of the present invention relates to a novel strategy for control of a variable geometry, or variable nozzle, turbocharger of an internal combustion engine. The disclosed strategy is implemented in a microprocessor-based engine control system, and utilizes certain data that is already available to the control system and/or developed by the processor. Certain data may be programmed into the control system.
Individual data may be categorized as: an input variable; a local variable; or an output variable. Input variables include barometric pressure; manifold pressure; engine load; and engine speed. Programmable parameters include an enable feature; high engine idle speed; and low engine idle speed. Each variable is calibrated in any suitable unit of measurement.
The input variables and the programmed parameters are applied to the general control strategy. The control operates on those variables and parameters in accordance with the general strategy to develop a PWM signal applied by a driver circuit to the solenoid that controls the turbocharger vane position.
One general aspect of the invention relates to control of a variable nozzle turbocharger of an internal combustion engine for changing boost according to changes in both engine speed and engine load to achieve desired boost appropriate to various combinations of engine speed and engine load so that boost appropriate to each particular combination is consistently achieved as the engine operates.
Another aspect relates to control of a variable nozzle turbocharger of an internal combustion engine for avoidance of turbine shaft speeds that exceed a predefined maximum.
Still another aspect relates to control of a variable nozzle turbocharger of an internal combustion engine for adjusting desired boost according to changing barometric conditions, like those that may be experienced when a vehicle being powered by such an engine is driven at different altitudes.
Still other aspects of the invention relate to details of the disclosed control strategy and its various sub-strategies. While the conditional integration provided by the P-LI-D control sub-strategy is useful in turbocharger boost control, it may provide advantages in other closed-loop control systems.
One general aspect of the claimed invention relates to an internal combustion engine comprising a turbocharger that creates engine boost and has a selectively positionable mechanism for controlling the amount of boost created by passage of exhaust gas through the turbocharger. A control selectively positions the mechanism to control the amount of boost in accordance with data inputs. The control comprises a processor for processing data, including the data inputs, to develop a control signal for selectively positioning the mechanism. A first data input to the processor comprises data corresponding to engine load, and a second data input to the processor comprising data corresponding to engine speed. A look-up table is programmed with values representing desired boost corresponding to sets of values representing various combinations of engine speed and engine load. A third data input to the processor comprises data corresponding to the amount of boost being created by the turbocharger.
The processor selects from the look-up table a value for desired boost corresponding to values of the first data input and the second data input. The processor processes the value of the third data input and the selected value for desired boost from the look-up table to generate error data defining error between the amount of boost being created by the turbocharger and the desired boost. The processor further processes the error data according to the value of the error data to cause the control signal to position the mechanism to reduce the error such that when the error data is less than a predetermined value, further processing comprises processing the error data with proportional, integral, and derivative control, and when the error data is not less than the predetermined value, the further processing comprises processing the error data with proportional and derivative control but without integral control.
Another general aspect of the claimed invention relates to an internal combustion engine comprising a turbocharger that creates engine boost and has a selectively positionable mechanism for controlling the amount of boost created by passage of exhaust gas through the turbocharger. A control selectively positions the mechanism to control the amount of boost in accordance with data inputs. The control comprises a processor for processing data, including the data inputs, to develop a control signal for selectively positioning the mechanism. A first data input to the processor comprises data corresponding to engine load, a second data input to the processor comprises data corresponding to engine speed, and a third data input to the processor comprises data corresponding to the amount of boost being created by the turbocharger. A first look-up table is programmed with values representing desired boost corresponding to sets of values representing various combinations of engine speed and engine load, and a second look-up table is programmed with values representing feed-forward values for use in developing the control signal: correlated with sets of values representing various combinations of engine speed and engine load. A function generator is programmed with values for turbocharger speed corresponding to values of boost for a given barometric pressure.
The processor selects from the first look-up table a value for desired boost corresponding to values of the first data input and the second data input, from the second look-up table, a feed-forward value corresponding to values of the first data input and the second data input, and from the function generator, a value for turbocharger speed corresponding to the value of the third data input. The processor processes the value of the third data input and the value of desired boost selected from the first look-up table to generate a value for error data defining error between the amount of boost being created by the turbocharger and the desired boost. The processor further processes the error data according to the value of the error data to create a first component of the control signal for causing the mechanism to reduce the error such that when the value of error data is less than a predetermined value, further processing comprises processing the error data with proportional, integral, and derivative control, and when the value of error data is not less than the predetermined value, the further processing comprises processing the error data with proportional and derivative control signal but without integral control. The processor processes the selected feed-forward value from the second look-up table to create a second component of the control signal, and the processor processes the selected turbocharger speed from the function generator to create a third component of the control signal for limiting turbocharger speed to a predetermined maximum speed during a condition when the control signal would otherwise be calling for a turbocharger speed greater than the predetermined maximum.
Another general aspect of the claimed invention relates to an internal combustion engine comprising a variable nozzle turbocharger powered by passage of exhaust gas through the turbocharger for creating and controlling engine boost and a control for controlling vane position of the variable nozzle turbocharger to control the amount of boost in accordance with data inputs. The control comprises a processor for processing data, including the data inputs, to develop a control signal for controlling the vane position.
The processor processes certain data to develop a value for desired boost and processes that value with a value corresponding to the amount of boost being created by the turbocharger to generate error data defining error between the amount of boost being created by the turbocharger and the desired boost, and the processor develops the control signal by further processing of the error data.
Still another general aspect of the claimed invention relates to an internal combustion engine comprising a device that comprises a selectively positionable mechanism in a flow path through the engine for controlling a pressure in the flow path. A control selectively positions the mechanism in accordance with data inputs. The control comprises a processor for processing data, including the data inputs, to develop a control signal for selectively positioning the mechanism. The processor generates error data for positioning the mechanism, and processes the error data according to the value of the error data to cause the control signal to position the mechanism to reduce the error such that when the value of error data is less than a predetermined value, the error data is processed using proportional, integral, and derivative control, and when the value of error data is not less than the predetermined value, the error data is processed using proportional and derivative control but without integral control.
Other general aspects of the claimed invention relate to the methods for controlling boost and pressure in engines as described above.
The foregoing, along with further aspects, features, and advantages of the invention, will be seen in this disclosure of a presently preferred embodiment of the invention depicting the best mode contemplated at this time for carrying out the invention. This specification includes drawings, briefly described below, and contains a detailed description that will make reference to those drawings.